1. Field of the Invention
The present inventions relates to brake pad assemblies for disc brakes in general and more particularly to a shim structure of a disc brake pad assembly for sound damping brake squeal noise in a disc brake apparatus.
2. Description of the Prior Art
Conventionally, in a disc brake apparatus two opposite brake pad assemblies compress a brake rotor in order to decelerate or stop the rotation of the brake rotor. The typical disc brake pad assembly 1, illustrated in FIGS. 1A and 1B, consists of a friction pad 4 attached by bonding to a face of a steel backing plate 2, which gives the friction pad 4 necessary support to resist a pressure load from a brake piston and/or caliper.
When the brake piston presses a back face of the backing plate 2 of the disc brake pad assembly 1 inwardly during the braking operation, an inner surface of the friction pad 4 is engaged in frictional, braking contact with the brake rotor of the disc brake apparatus. Such an action creates high operating temperatures of the disc brake apparatus (500 C.° or more) and high specific area pressures (about 1000 kg/cm2) as the brake piston normally has a relatively small cross section. The friction between the brake rotor and the brake pad assembly generates vibration of the elements of the brake pad assembly during braking operation. As a result, unpleasant and often loud braking noise, particularly relatively high pitched and undesired brake “squeal” noise, frequently occurs during the braking operation.
Numerous solutions to the brake noise problem have been proposed, many of which rely on the principle of damping vibrations. One of the most common solutions known in the art is placing of a noise-damping shim 6 (as illustrated in FIGS. 1A and 1B) in the form of a plate-like piece having a vibration-damping characteristic, between the backing plate of the brake pad assembly and the piston or caliper of the disc brake apparatus.
While known solutions to the brake noise problem, including but not limited to the noise-damping shims discussed above, have proven to be acceptable for various disc brake applications, such devices are nevertheless susceptible to improvements that may enhance their performance, cost and packaging. With this in mind, a need exists to develop improved anti-squeal shims for the disc brake apparatuses that advance the art.